In a filter arrangement of the type generally referred to above, the gauze placed in front of the screen prevents a flicker effect which can be seen especially in the display of small data characters on the screen. If the image is observed through the gauze, it is undisturbed as a whole and it is guaranteed that data is evaluated via a data display unit with less fatigue.
The number of characters which can be represented on the screen of a cathode ray tube in data display units is constantly being increased by the improvement of opto-electronic means, so that at the present time several thousand characters can be represented on the screen simultaneously. It is frequently necessary for the operating personnel to observe the screen for the whole day or, alternately, compare text originals with the screen text. Due to the constant increase in the number of characters which can be displayed, the quality of graphic representation also has to be continuously improved. For this purpose, on the one hand, opto-electronic improvements can be introduced and, on the other hand, certain representational colors and contrast values can be selected, in order to make even the smallest characters optimally perceptible and, consequently, also guarantee evaluation without fatigue over a long period.
Thus, it is known, for example, to use for the display of characters on a screen those colors which are adapted to maximal visual discrimination. If, at the same time, the afterglow time is adapted to the properties of the human eye by selecting a suitable phosphor for the screen of the cathode ray tube, it is then possible to obtain optimal representation of characters with the avoidance of afterglow effects.
An especially favorable type of representation exists when yellow characters are displayed on an amber-colored background. This is attributable to the fact that yellow light lies in the region of peak sensitivity of the human eye and can still be perceived clearly even in the case of attenuated representation. If the image background is simultaneously brightened, the reduction in contrast associated therewith lengthens the life of the cathode ray tube.
The problem of the invention is to specify a filter arrangement for a cathode ray tube, which embodies a color filter pane and a mounting structure for disposition of the tube within a case.
This is accomplished by means of the combination of a case having lateral and circumferentially forward structure elements adjacent the tube, a pane of filtering material such as acrylic plastic, and a sealing gasket which grips the edge of the pane and serves the dual function of holding the tube in the proper spaced relation with both the pane and the case. In addition the pane bears directly against the forward structure of the case.
In the preferred form, the gasket comprises a gripping portion of higher hardness and a tubular, cushioning portion of lower hardness, the two portions being integral or substantially integral with one another.